Means for circulating fluids



May 10, 1938. K. P. BRACE Er AL 2,116,958

MEANS FOR CIRCULATING FLUIDS Filed April 19, 1935 2 Sheets-Sheet l3nventor4 ffemperPBrace RObertBPQr'a 0rd 5 W (Ittomeg May 10, 1938. BRAEET AL 2,116,958

1 MEANS FOR CIRCULATING FLUIDS Filed April 19, 1935 2 Sheets-Sheet 23nnentoud ffemperPBrace Zfioberfli POmwfard Gttorneg Patented May 10,1938 PATENT OFFICE MEANS FOR CIROULATING FLUIDS Kemper l. Brace andRobert B. P. Crawford, Washington, D. 0.

Application April 19, 1935, Serial No. 17,368

This invention deals with the forced circulation of fluids and moreparticularly with the propulsion of one liquid into another under ahigher pressure without the employment of pumps or other mechanicalmoving parts. An object of the invention is to provide a method andapparatus for continuously concentrating a solun For solutions, ofnon-electrolytes such as cane equal to the prestion.

sure of any solution depends upon the co'ncenv tion which is beingcontinuously diluted and for continuously diluting a solution which isbeing continuously concentrated thereby maintaining the degree ofconcentration substantially con-. stant.

A further more specific object is to provide a method and means for.supplying liquid to a boiler without the use of a pump or othermechanical moving mechanism.

A still further more specific object is to provide a method andapparatus for pumping the liquid in an absorber type of refrigeratorfrom the absorber into the boiler without the use of mechanical pumpsand without the use 01' hydrogen or other gases commonly used to balancethe pressures in systems of this kind.

Further objects and advantages will become apparent as the descriptionproceeds.

Referring to the accompanying drawings which are made a part hereof andon which similar are used to denote the same reference characters partthruout,

Figure 1 is a view in elevation of one of the simplest forms ofapparatus embodying the invention,

Figure 21s a view in elevation of a refrigerating system of the absorbertype showing the application of the invention,

Figures 3 and 4 are modified forms of refrigerating apparatus showingthe invention.

It is well known that if a pure solvent is separated from a solution ofa solute in the same solvent by a semi-permeable membrane, there will bea flow of solvent thru the membrane into the solution. This flow willoccur even when the pressure upon the solution is much greater than thepressure upon the solvent. The pressure necessary to be applied to thesolution to prevent.

this fiow is called the osmotic pressure of the solu- As would beexpected, the osmotic prestration of the solution, that. is, the higherthe concentration, the higher the osmotic pressure.

sugar, the osmotic pressure is sure which an equivalent gram molecularvolume of the solute would exert if confined to the space occupied bythe solution. Due to the eflfect of ionization, the osmotic pressure ofelectrolytes such as NaCl, NaOH, LiC'l, etc., is as a rule considerablyhigher than that of non-electrolytes of the same concentration. Ithasibeen found that for any substance, whether it is an electrolyte orFrom the above formula it can be readily seen that the osmotic pressureof any solution which is of suflicient concentration to lower the vaporpressure appreciably of the solvent is very high. For example, the.osmotic pressure of a six molar (67%) sugar solution is 232 atmospheresor 3410 lbs. per square inch whereas the vapor pressure lowering of asix molar sugar solution L L'L pc is only 20% at 70 degrees F.

The fact that the osmotic pressure of a six molar sugar solution isequal to 3410 lbs. per square inch means that if a semi-permeablemembrane separates the solution from pure solvent, that is, frompurewater, a pressure of 3410 lbs. per square inch would have to beappliedto the solution to prevent water from passing thru the membraneinto the solution.

11' instead of separating a solution from a pure solvent, a solution isseparated from a stronger solution by meansoi' a semi-permeablemembrane, there will be a flow of pure solvent from the weakersolutionto the stronger and the pressure causing the flow is equal to thedifference between the osmotic vpressures of the two solutions. The flowwill continue until the concentration of the two solutions is the same,that is until both solutions have the same osmotic pressure.

Now if the stronger solution is continually concentrated by boiling oil?the solvent and the weaker solution dition of pure solvent, then theflow of pure solvent" thru the membrane from the weaker solution to thestrong solution will continue as long as there is a difference inconcentration.

Figure 1 shows one of the simplest embodiments of the invention in theform of apparatus for continuously concentrating a solution which isbeing continuously diluted and for diluting a solution which is beingcontinuously concentrated. Vessels Ill and l l contain weak solution I2- and strong solution l3 respectively of some non-volatile solute in asuitable solvent, such for is continually diluted by the adexample ascane sugar in water. The solutions are separated by a semi-permeablemembrane 15. Pure solvent may be boiled ofi from the strong solution I3by heating element 14, thereby concentrating the solution and puresolveht'may be supplied by pipe [8 to the solution 12 to dilute thisweak solution. So long as the concentration of the solution 13 isgreater than the concentration of the solution 12 there will be a flowof pure solvent thru the semi-permeable membrane from chamber 18 into.chamber ll.

We may assume that the solution 12 is a 1.0 molar solution of cane sugarin water and that the solution 13 is a six molar solution of cane sugarin water. The osmotic pressure of a six molar solution is 3410 lbs. persquare inch. The osmotic pressure of a 1.0 molar solution is 397 lbs.per square inch. Therefore, the force driving pure solvent (water) fromthe weak solution 12 into the strong solution 13 is 3410 minus 397 lbs.per square inch or3013 lbs. per square inch, and nothing will stop theflow of solvent from the weak into the strongsolution except an externalpressure on the strong solution of 3013 lbs. per square inch. It isapparent from the foregoing that a semi-permeable membrane providesmeans for causing a solvent to flow from a weak solution under a lowpressure to a strong solution under a. high pressure without the aid ofa mechanical pump. Pressure may be built up in the boiler by providing athrottling valve 11.

From the structure described it will be apparent that the device mayhave many possibilities in its adaptation to useful purposes. Forexample, if the vapor under pressure from the boiler is conducted to afluid motor the device may serve as a boiler for an engine in which theboiler is fed without the use of mechanical pumps or injectors.

Figure 2 shows the invention adapted to a refrigerating system of theabsorber type. In this form of refrigerator a vapor is absorbed into asolution. As here shown numeral 18 indicates an evaporator, 19 anabsorber, 20 a boiler, 2i a condenser, 22 a vapor conductingconnectionfrom the boiler to the condenser and 123 a connection from thecondenser to the evaporator. v Vapor is boiled ofi by a heater 2 1. Acooling coil 25 cools the liquid in the absorber. This cooling coil maybe supplied with cooling water which passes thru 'pipe 26 to thecondenser after leaving coils 25. If

preferred both the cooler 25 and the condenser may be air cooled; :suchcooling systems are well known and therefore need not be here described;

Before starting, the boiler will be partially filled with asuitablesolntion. .This may be a solution of cane sugar and waterasstated in the description of the system shown of any suitablenon-volatile solute, such as NaOH,

.LiCl, H2804, Lil, ZnCl, etc., in a solvent.

Numeral 21 indicates the strong solution in the boiler, 28 a weaksolution in the absorber and 29 the pure solvent in the evaporator.There will be a body of solvent'vapor 30 above the body .of solvent inthe evaporator. The upper portion of the evaporator communicates withthe upper portion of the absorber thru a passage 3|. A semipermeablemembrane 32 separates the strong solution 21 in the boiler from the weaksolution 28 in" the absorber. Suitable examples of such membranes arecollodion, parchment, animal intestine, animal bladder, fish skin,rubber,-copper ferrocyanide precipitated in porous earthenware,porcelain, ground glass, gelatine, etc.

After filling the system to the desired levels hfFigure 1, or a solutionwith the solutions and solvent, all air and other foreign gases areevacuated from the system and the system closed. The evaporator will besurrounded by or in heat exchange relation with the media to be cooled.Heat extracted from this medium will evaporate the refrigerant. Now thevapor pressure above the pure solvent 28 is greater than the vaporpressure above the weak solution 28. There will therefore be a flow ofvapor from chamber 18 thru channel 8| into chamber 19, this vapor beingabsorbed into the solution 28. This evaporation of vapor from thesolvent body 28 and absorption into 28 will cause the temperature in 18to fall and the temperature in IS to rise. The added heat in solution 28may be carried ofl by'the cooling coil 25. The addition of pure solventto the weak solution 28 will tend to dilute this solution. But thesolution in the boiler 20 is stronger than the solution 28. There will,therefore, be a flow of pure solvent thru the semi-permeable membrane 82from the body of solution 28 into the solution 21. The heater 24continuously boiling of! pure solvent from the solution 21 continuouslyconcentrates this solution. The addition of pure solvent from absorber19 will tend to keep the solution at the same degree of concentration.

The rate of flow of pure solvent from I8 to 28 is directly proportionalto the difierenoe between the osmotic pressures of the solutions 21 and28 minus the difference in total pressure in vessels i9 and 211. Thus ifthe solution 28 is a 1.0 molar sugar solution having an osmotic pressureof 397 lbs. per square inch and solution 21 is a 6 molar sugar solutionhaving an osmotic pressure of 3410 lbs. per square inch and if thepressure above the two liquids be ignored for the present, there will bea difference in pressures of 3410 minus 397, or 3013 lbs. per squareinch and this will represent the force driving the pure solvent fromsolution 28 intosolution 21.

For practical purposes a solution of sodium bycane sugar solution. Letus assume, therefore,

. that water and NaOH are the solvent and 'the solute-respectively. Letus assume that the temperature desired in the evaporator is 40 degreesF. and that the temperature of the tap water for cooling coil 25 is '10degrees. Now the vapor pres sure of water at 40 degrees is 6.4 mm. ofHg'and therefore in order for the-water 29 in the evaporator 18 to boilat 40, the vapor pressure of the solution 28 in the-absorber 19 must beless'than' 6.4 mm. of Hg at a temperature slightly in ex- "cess of 70degrees (say perhaps degrees). Ex-

perimental data show that the vapor pressure of a 40% solution of NaOHin water exerts a vapor pressure of 5.3 mm. of Hg. at 80. Y Therefore,we can assimie that the concentration of the solution 28 is 40% and thatthe driving force causing solvent vapor (water) to pass from l8 to'l9 as6.4-5.3,that is as 1.1 mm. of mercury. Withan unrestricted passage 31between the chamber 18 and the chamber 19 water vapor will pass at arapid rate from 29 to 28 and the temperature of 29 will be maintained at40 degrees as long as the temperature of the solution 28 is kept at 80degrees and the concentration at 40%.

greater than'28. Let us assume that the concen- 7 sorber and theconcentrator or boiler.

permeable membraneous material tration of 21 is 50% by weight. By theformula given, the osmotic pressure of a 40% solution 28 at 80 degreesF. is 28,300 lbs. per square inch. The osmotic pressure of a 50%solution 21 at 165 degrees F. (B. P. at 36 mm. Hg) is 35,750 lbs. persquare inch. The difl'erencebetween the osmotic pressure of solution 21and solution 28 is 7,450 lbs. per square inch. Experimental dataindicate that the amount of semi-permeable membrane required for a 100lb. ice box is five square feet.

Figure 3 showsa form of the invention in which an interchanger 40 ispositioned between the concentrator and the absorber. It will be notedthat there is a temperature difference of about 85 degrees between theconcentrator and the absorber. It is advisable to prevent a loss of heatfrom the concentrator to the absorber. The interchanger is designed toreduce the heat loss as far as possible, and thereby increase theemciency of the system. Numerals 4|, 42, 48 and 44 denote the condenser,the evaporator, the ag- T e evaporator contains pure solvent 45, theabsorber contains weak solution 46 and the boiler a strong solution 41.Solvent is boiled off by heater 48. Cooling water for the cooler 48 issupplied thru pipe 50 the water leaving thru pipe after passing thru thecondenser 4| to condense the vapor from the boiler. Both cooler 48 andcondenser 4| may be air cooled if desired.

The upper portion of the evaporator chamber is connected by pipe 52 witha pipe 58 which extends down into the weak solution 46 and terminates ina header 54 which is perforated to permit vapor to pass into thesolution 46 and be absorbed therein. The absorber is connected by pipes55 and 56 with a chamber 51 thru which the weak solution is circulatedby convection.

A chamber 58 is positioned within the chamber- 51 and its walls areformed partially from semi- 59. The strong solution in the boiler iscirculated thru the chamber 58 passing from the boiler thru pipe 63thence thru the interchanger 40, pipe 60, pipe 61, back thru theinterchanger 40 and pipe 62 into the boiler. A water jacket 64 may beplaced about the pipe 60 to cool the strong solution before it entersthe chamber 58. This jacket may be supplied with water from the coil orwater cooling jacket 48.

The heater may include a flue 61 which passes up thru the boiler toeffect better heating.

Refrigerant vapor driven oi the boiler passes thru pipe '65, condenser4| and into receiver 66. In order to insure that only liquid refrigerantshall pass from the receiver to the evaporator a valve 68 operated by afloat 69 controls passage of refrigerant to the evaporator.

Any suitable refrigerant may be used. For domestic refrigeratorsrequiring evaporator temperature of 20 degrees or lower it is believedthe most satisfactory solution would be a solution of ammoniumthiocyanate (NHiCNS) in liquid ammonia (NH:). v

Let us assume that the temperature desired in the evaporator is 15degrees F. and that the temperature of the tap water or cooling air,when air is used, is 90 degrees. We will assume that the cooler 48 islarge enough to maintain a temperature of 100 degrees in the weaksolution 46. We will assume also that the cooling water in passing thruthe cooler 48 is heated to approximately 100 degrees and that it iseflective to condense the ammonia in the condenser at a temperature of110 degrees.

Now the vapor pressure of pure ammonia 45 in the evaporator 42 at 15degrees F. is 2100 mm. of Hg. In order to have a flow of vapor from theevaporator to the absorber the vapor pressure of the weak absorbingsolution must be less than the vapor pressure of the pure solution. Thevapor pressure of a 60% solution of NHCNS in ammonia at 100 degrees F.is approximately 2000 mm. of Hg. This gives us a vapor pressurediiference between the evaporator and the absorber of 100 mm. of Hg. Wemay therefore assume that the weak solution 46 is a 60% solution ofNH4CNS in NH3. According to the formula the osmotic pressure of a 60%solution of NH4CNS in NH; at 100 degrees F. is 40,719 lbs. per squareinch. Assume that the strong solution 41 in the boiler is an 80%solution of NH4CNS in NHa. From the formula we note that the osmoticpressure of an 80% solution of NHiCNS in NH: at 100 degrees F. is 49,677lbs. per square inch. It should be noted that the strong solution whichis circulated from the boiler is cooled by the jacket 64 and by the bodyof weak solution at 100 degrees temperature which surrounds the chamber58.

Now as we have stated above, the vapor pressure above the weak solution46 is 2000 mm. of Hg or about 38 lbs. per square inch. The vaporpressure above the strong solution is the vapor pressure of pure ammoniaat condenser tempera- .ture, which as we-have stated is 110 degrees F.

This vapor pressure is about 250 lbs. per square inch. The force tendingto drive pure ammonia liquid from the weak solution into the strong is(49,677+38) (40,719+250) =8746 lbs. per square inch It is thereforeapparent that in spite of the pressure difference of 212 lbs. in theboiler and the absorber pure liquid will flow from the absorber into theboiler at a rapid rate thru the semipermeable membrane due to osmoticforce.

Figure 4 shows another embodiment of the invention. Numerals 10, 1| and12 represent the evaporator, the boiler and the absorber. The absorberconsists of a plurality of tubes having walls of semi-permeablemembraneous material connecting headers!!! and 82. This absorber ispositioned in a chamber 13 where it is enveloped in vapor passing fromthe evaporator thru passage 14. The solution circulating by convectionthru the absorber is cooled by air cooler 15 of any suitable sort. Puresolvent vapor in chamber 13 will be absorbed thru the walls of the tubesand will tend to dilute the solution therein. To maintain the properdegree of concentration in the tubes, a portion of the solution iscirculated thru the boiler thru pipes 11,18 and interchanger 18. Thiscirculating solution is cooled by air cooler 16. This pipe 18 may becoiled around the flue 80 to effect better heating.

The boiler will be partially filled with a suitable solution. This maybe a solution of NHACNS in NHa. The pure solvent in the evaporator maybe liquid ammonia 82. Ammonia vapor boiled ofi from the boiler will passthru pipe 93, be condensed by air condenser 83 and delivered to receiver84. A valve 85 controlled by bellows 86 will control passage of liquidfrom pipe 81 to pipe 88 so .as to prevent the passage of gas to theevaporator- Pressure in the bellows and pressure below the valve will beequal since both are subject to the pressure in the condenser thru pipes81 and 88 so that'the valve 85 will be closed by gravity. When liquidaccumulates in the leg 88 of the U-tube this will unbalance the valveand permit liquid refrigerant to pass thru the valve into the line 89.

Instead of the pressure operated valve Just described we may use thefloat controlled valve shown in Figure 3.

Assume that a temperature of 15 degrees F. is desired in the evaporatorand that the cooling media for the absorber is at a 90 degreetemperature and that the coolers are sufflciently large to maintain atemperature of 100 degrees in the absorption solution and a temperatureof 110 degrees in the condenser. We will assume, as stated above, thatthe solution Si is a 60% solution of NHlCNS in NIB. Now, as we havestated, the

vapor pressure of pure ammonia at 15 degrees is 2100 mm. of Hg. Thevapor pressure of a 60% solution of NH4CNS in NH: at 100 degrees F. is2000 mm. of Hg. The osmotic pressure of a 60% solution of NHrCNS in NH:is 40,719 lbs. per square inch. Since there is a pressure in theabsorber chamber 13 outside the tubes of about '38 lbs. per square inchthe total force tending to drive the pure solvent into the solution thruthe semi-permeable membrane is I 40,757 lbs. per square inch. But thevapor pressure of the pure ammonia in the condenser is the vaporpressure at a temperature of 110 degrees which is about 250 lbs. persquare inch. Taking this from the pressure indicated above, since thisis a pressure acting against the flow of solvent into the strongsolution, we have a total pressure acting to drive solvent vapor intothe solution of 40,507 lbs. per square inch. 8

From the foregoing it will be apparent that we have a system in whichthe solvent will be automatically supplied to the boiler and that thesystem will operate continuously without the necessity of a pump or thepresence of an inert gas to balance pressures.

It will be obvious to those skilled in the art that various changes maybe made in the invention without departing from the spirit thereof. We,therefore, do not limit ourselves to the invention as shown in thedrawings andas described in the specification but only asset forth inthe appended claims.

What we claim is:

1. A device of the kind described comprising a vessel having acompartment therein having a solution of a pure solvent and anonvolatile solute dissolved therein, a second compartment having a bodyof pure-solvent therein under a pressure less than that in the firstnamed compartment,

a semi-permeable membrane separating the two bodies of liquid to-cause aflow of solvent by osmosis into the solution, means for boiling oflsolvent from the solution and means for supplying pure liquid solvent tothe body of pure solvent.

2. A device of the kind described comprising a vessel divided into twochambers by a semi-permeable membrane, a concentrated solution of, asolvent and a nonvolatile solute in one chamber, a less concentratedsolution of the composition in the other chamber, and a third chamberhaving a body of-pure solvent therein, the space above said last namedsolvent being opento the space above the weaker solution to permitpassage of vapor from said solvent to the said solution to be absorbedtherein, the semi-permeable membrane causing osmotic flow of puresolvent from the weaker to the stronger solution.

3. A refrigerator of the absorber type comprising a boiler, an absorber,an evaporator, a condenser and heater, the boiler having therein astrong solution of a solvent and a non-volatile solute, the absorberhaving therein a weaker solution of the same solvent and solute, meansfor conducting vapor from the evaporator into the weaker solution tohave it absorbed therein, means for circulating said weak solution andfor cooling it, a semi-permeable membrane separating the weak from thestrong solution, means for circulating said strong solution in surfacecontact with said membrane to circulate the pure solvent absorbed fromthe weaker solution and bring it into the boiler to dilute the solutiontherein which is being continuously concentrated by boiling oif puresolvent therefrom.

4. A refrigerator of the absorber type comprising. a boiler, anevaporator, an absorber, a plurality of tubes positioned in the saidabsorber, said tubes being filled with a solution of a solute and asolvent, said tubes being exposed to solvent vapor from the evaporator,said tubes having walls of semi-permeable membranes to cause the solventto flow by osmosis from the absorber to the solution, means forcarrying. of! heat from the solution, and means for circulating saidsolution thru the boiler, and means for boiling of! pure solvent fromthe solution, for condensing it and returning it in liquid form to theevaporator.

5. A refrigerating system of the absorber type comprising a still, anabsorber, an evaporator, a condenser, and a semi-permeable membraneseparating vapor of the pure solvent in the evaporator from solutioncirculated from the still, a liquid trap between the condenser andevaporator, and a pressure controlled balanced valve operable upon arise of liquid in the trap for returning only liquid refrigerant to theevaporator.

.6. A device of the kind described comprising a pair of chambers, onecontaining a solution of a volatile solvent and a non-volatile solute,the other containing a body of the solvent substan-, tially free of thesolute and under a pressure less than the pressure in the first namedchamber, a semi-permeable membrane separating the solution from vapor ofthe body of pure solvent, and means for vaporizing solvent from thesolution in the first named chamber, condensing it, and delivering it tothe body of solvent in the other chamber, the said membrane causing puresolvent to flow by osmosis from the body ofpure solvent to the solution.r

'1. A refrigerating system of the kind described comprising a boilercontaining a solution of a solute and a volatile solvent, a chamber,having walls of semi-permeable membraneous material, in communicationwith the solution in the boiler, thermal means for circulating thesolution from the boiler thru the said chamber, an evaporator, means forboiling off vapor from the solution, condensing it and delivering it tothe said evaporator, means for conducting refrigerantvapor from saidevaporator into surface contact with said semipermeable membraneouswalls while maintaining said vapor under pressure appreciably lower thanthe pressure in said chamber, the solvent vapor being caused to flow byosmosis only thru the semi-permeable membraneous walls of the saidchamber into the solution in said chamber.

KEMPER P. BRACE. ROBERT B. P. CRAWFORD.

